IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0

=============================================
[ INFO: possible recursive locking detected ]
4.9.99-gc2f9bce #22 Not tainted
---------------------------------------------
syz-executor4/3960 is trying to acquire lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff830b1837>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
but task is already holding lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff830b1837>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(rtnl_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor4/3960:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff830b1837>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (ipvs->sync_mutex){+.+.+.}, at: [<ffffffff832df74d>] do_ip_vs_set_ctl+0x90d/0xbd0 net/netfilter/ipvs/ip_vs_ctl.c:2397

stack backtrace:
CPU: 0 PID: 3960 Comm: syz-executor4 Not tainted 4.9.99-gc2f9bce #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8b67410 ffffffff81eb0f09 ffffffff8559cf30 ffffffff8559cf30
 ffffffff8559cf30 ffff8801d8f0d0e8 bdd6c1b1fa547de9 ffff8801d8b675d0
 ffffffff814258ff ffffffff84e98ca0 ffffffff851f0ea8 ffffffff84e98ca4
Call Trace:
 [<ffffffff81eb0f09>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0f09>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814258ff>] print_deadlock_bug kernel/locking/lockdep.c:1727 [inline]
 [<ffffffff814258ff>] check_deadlock kernel/locking/lockdep.c:1771 [inline]
 [<ffffffff814258ff>] validate_chain kernel/locking/lockdep.c:2249 [inline]
 [<ffffffff814258ff>] __lock_acquire.cold.59+0x166/0x5f8 kernel/locking/lockdep.c:3345
 [<ffffffff81238e60>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff839e9920>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff839e9920>] mutex_lock_nested+0xc0/0x870 kernel/locking/mutex.c:621
 [<ffffffff830b1837>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 [<ffffffff8343b04c>] ip_mc_drop_socket+0x8c/0x230 net/ipv4/igmp.c:2635
 [<ffffffff8341c6eb>] inet_release+0x5b/0x1d0 net/ipv4/af_inet.c:420
 [<ffffffff8300fab6>] sock_release+0x96/0x1c0 net/socket.c:599
 [<ffffffff832f29ee>] start_sync_thread+0xa0e/0x1ea0 net/netfilter/ipvs/ip_vs_sync.c:1926
 [<ffffffff832df75f>] do_ip_vs_set_ctl+0x91f/0xbd0 net/netfilter/ipvs/ip_vs_ctl.c:2398
 [<ffffffff831daedd>] nf_sockopt net/netfilter/nf_sockopt.c:105 [inline]
 [<ffffffff831daedd>] nf_setsockopt+0x6d/0xc0 net/netfilter/nf_sockopt.c:114
 [<ffffffff83344ada>] ip_setsockopt+0x9a/0xb0 net/ipv4/ip_sockglue.c:1249
 [<ffffffff833f2f7a>] udp_setsockopt+0x4a/0x90 net/ipv4/udp.c:2088
 [<ffffffff835afd2a>] ipv6_setsockopt+0x10a/0x130 net/ipv6/ipv6_sockglue.c:901
 [<ffffffff835bf76a>] udpv6_setsockopt+0x4a/0x90 net/ipv6/udp.c:1351
 [<ffffffff8301975a>] sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:2706
 [<ffffffff83016516>] SYSC_setsockopt net/socket.c:1772 [inline]
 [<ffffffff83016516>] SyS_setsockopt+0x166/0x260 net/socket.c:1751
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
IPVS: stopping backup sync thread 3963 ...
IPVS: stopping backup sync thread 3964 ...
IPVS: stopping backup sync thread 3966 ...
IPVS: stopping backup sync thread 3969 ...
IPVS: stopping backup sync thread 3976 ...